Department of Family Medicine and Public Health, University of California San Diego, San Diego, California, 92093, USA.
Center for Behavioral Epidemiology and Community Health (CBEACH), San Diego State University, San Diego, CA, 92123, USA.
Int J Behav Nutr Phys Act. 2020 Jul 9;17(1):88. doi: 10.1186/s12966-020-00992-x.
Sedentary behavior (SB) is linked to negative health outcomes in older adults. Most studies use summary values, e.g., total sedentary minutes/day. Diurnal timing of SB accumulation may further elucidate SB-health associations.
Six thousand two hundred four US women (mean age = 79 ± 7; 50% White, 34% African-American) wore accelerometers for 7-days at baseline, yielding 41,356 person-days with > 600 min/day of data. Annual follow-up assessments of health, including physical functioning, were collected from participants for 6 years. A novel two-phase clustering procedure discriminated participants' diurnal SB patterns: phase I grouped day-level SB trajectories using longitudinal k-means; phase II determined diurnal SB patterns based on proportion of phase I trajectories using hierarchical clustering. Mixed models tested associations between SB patterns and longitudinal physical functioning, adjusted for covariates including total sedentary time. Effect modification by moderate-vigorous-physical activity (MVPA) was tested.
Four diurnal SB patterns were identified: p1 = high-SB-throughout-the-day; p2 = moderate-SB-with-lower-morning-SB; p3 = moderate-SB-with-higher-morning-SB; p4 = low-SB-throughout-the-day. High MVPA mitigated physical functioning decline and correlated with better baseline and 6-year trajectory of physical functioning across patterns. In low MVPA, p2 had worse 6-year physical functioning decline compared to p1 and p4. In high MVPA, p2 had similar 6-year physical functioning decline compared to p1, p3, and p4.
In a large cohort of older women, diurnal SB patterns were associated with rates of physical functioning decline, independent of total sedentary time. In particular, we identified a specific diurnal SB subtype defined by less SB earlier and more SB later in the day, which had the steepest decline in physical functioning among participants with low baseline MVPA. Thus, diurnal timing of SB, complementary to total sedentary time and MVPA, may offer additional insights into associations between SB and physical health, and provide physicians with early warning of patients at high-risk of physical function decline.
久坐行为（SB）与老年人的健康状况不佳有关。大多数研究使用总时长等综合值来衡量 SB，例如每天的久坐总时长。SB 积累的昼夜时间分布可能进一步阐明 SB 与健康的关联。
本研究纳入了 6204 名美国女性（平均年龄=79±7 岁；50%为白人，34%为非裔美国人），她们在基线时佩戴加速度计进行了 7 天的监测，共获得了 41356 人天，其中 600 分钟/天以上的数据超过了 600 分钟。在 6 年的时间里，参与者还接受了年度健康随访评估，包括身体机能。采用一种新的两阶段聚类程序来区分参与者的昼夜 SB 模式：第一阶段使用纵向 k-均值对日间 SB 轨迹进行分组；第二阶段根据第一阶段轨迹的比例使用层次聚类来确定昼夜 SB 模式。混合模型检验了 SB 模式与纵向身体机能之间的关联，调整了包括总静坐时间在内的混杂因素。并检验了中度到剧烈体力活动（MVPA）的调节作用。
确定了四种昼夜 SB 模式：p1=全天高 SB；p2=较低清晨 SB 的中度 SB；p3=较高清晨 SB 的中度 SB；p4=全天低 SB。较高的 MVPA 可减缓身体机能下降的速度，并与各模式下较好的基线和 6 年身体机能轨迹相关。在低 MVPA 中，p2 与 p1 和 p4 相比，6 年身体机能下降更明显。在高 MVPA 中，p2 与 p1、p3 和 p4 相比，6 年身体机能下降相似。
在一个大型的老年女性队列中，昼夜 SB 模式与身体机能下降率相关，独立于总静坐时间。具体而言，我们发现了一种特定的昼夜 SB 亚型，其特征是在一天中较早的时间有较少的 SB，而在较晚的时间有更多的 SB，在基线 MVPA 较低的参与者中，身体机能下降最快。因此，SB 的昼夜时间分布，与总静坐时间和 MVPA 相辅相成，可能为 SB 与身体健康之间的关联提供更多的见解，并为医生提供身体机能下降高风险患者的早期预警。
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